C Exercises: String representation of common directory paths

Last update on August 08 2025 12:53:20 (UTC/GMT +8 hours)

16. Common Directory Tree

A set of strings represent directory paths and a single character directory separator (/).
Write a program in C language to get a part of the directory tree that is common to all directories.
Test Data:
({/home/me/user/temp/a", "/home/me/user/temp/b","/home/me/user/temp/c/d"}) ->
/home/me/user/temp

Sample Solution:

C Code:

#include <stdio.h>

int common_path(const char *const *names, int n, char sep)
{
	int i, pos_len;
	for (pos_len = 0; ; pos_len++) {
		for (i = 0; i < n; i++) {
			if (names[i][pos_len] != '\0' &&
					names[i][pos_len] == names[0][pos_len])
				continue;
			while (pos_len > 0 && names[0][--pos_len] != sep);
			return pos_len;
		}
	}
	return 0;
}
int main()
{
	const char *names[] = {
		"/home/me/user/temp/a",
		"/home/me/user/temp/b",
		"/home/me/user/temp/c/d",
	};
	int len = common_path(names, sizeof(names) / sizeof(const char*), '/');
	if (!len) 
	   printf("No common path\n");
	else 
	  printf("Common path: %.*s\n", len, names[0]);

	return 0;
}

Sample Output:

Common path: /home/me/user/temp

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to compare multiple directory paths and output the longest common prefix.
Write a C program to extract the common subdirectory from a list of file paths with different separators.
Write a C program to parse directory paths and display the directory tree structure that is shared by all paths.
Write a C program to find the common root directory from a list of absolute paths and print it in normalized form.

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